I've had a BearShare Pro 5.0.2.3 connected to me for over 4 days as a leaf. The only reasons they would not become an ultrapeer are (1) they set the program not to become an ultrapeer, or (2) they are firewalled.
BearShare versions prior to 5.2 definitely did not have UPnP support & need to be 'port forwarded' so BS is not being impeded by a firewall blocking its incoming & outgoing TCP & UDP messages. This includes the BS 5.1 beta version.
And it's my guess if you are an ultrapeer but connected to less than 5 Leaves, then you are firewalled. Try to fix the this! Yes, port forwarding. It works, so don't hesitate in trying! You'll be surprised by the difference when not firewalled.